1. Technical Field
The present invention relates to methods of recovering free fatty acids from edible oils and more particularly to methods of recovering free fatty acids having a low ester content and high acid value from oils.
2. Description of the Related Art
It is known that edible oils, e.g., vegetable and animal oils, may be deodorized to remove impurities, e.g., volatiles, colored components, and odiferous compounds, to provide oils of higher quality. Deodorization of these oils through water vapor distillation produces steam distillates. A typical steam distillate from a vegetable oil, i.e., vegetable oil distillate, such as soybean oil, contains tocopherols, sterols, fatty acids, glycerides and other components. Among these various components, the tocopherols which include alpha-, beta-, gamma-, and delta-tocopherols, are of commercial value because of their vitamin E activity, i.e., antioxidizing activity. Accordingly, various commercial processes including esterification, saponification, fractional extraction, etc., exist for recovering tocopherols from the steam distillates.
Saponification is a particularly preferred method, since it produces salts of fatty acids (soaps) which can be readily separated from unsaponifiables, e.g., tocopherols and sterols, which are present in the steam distillates, through the use of, e.g., a solvent which dissolves the tocopherols but not the salts, thereby allowing recovery of tocopherols free from fatty acids. Typically, the steam distillate is saponified by heating the distillate with alkali metal hydroxide in an alkanol-water mixture. The saponified mixture is then subjected to solvent extraction using a solvent which extracts the non-saponifiables, e.g., tocopherols and sterols, to produce a phase containing mainly the non-saponifiables and solvent and a raffinate phase containing saponified fatty acids, water, alkali metal hydroxide, alkanol, and the remaining solvent. The phase containing the non-saponifiables, e.g., tocopherols, can then be readily separated from the raffinate phase to provide tocopherols free from fatty acids. The tocopherols can then be further processed for commercial use.
The fatty acids which are a by-product of the tocopherol recovery method, also have commercial value in a wide range of applications which include, inter alia, soaps, foods, cosmetics, paints and protective coatings, lubricating greases and oils, etc. The recovery of free fatty acids from the raffinate phase typically involves acidulation of this phase to produce an aqueous layer containing salt and an organic layer containing the free fatty acids, alkanol, and solvent. The alkanol and solvent are then removed from the organic layer by stripping at relatively high temperatures, e.g., by sending the organic layer through a heat loop having a temperature of about 150xc2x0 C. prior to sending the organic layer to an atmospheric flash tank. The stripped fatty acids can then be sent through a counter-current stripper with steam to further reduce solvent and alkanol present in the mixture.
A problem encountered in utilizing the aforementioned stripping process is that when the organic layer is sent through the heat loop maintained at relatively high temperatures of about 150xc2x0 C., the free fatty acids undergo esterification with the alkanols present in the organic layer. The esterification of the fatty acids becomes significant enough to have a detrimental effect on the quality of the resultant fatty acid product. Typically, the free fatty acids recovered from such a stripping process have an ester content of from about 1.5 to about 5.0 weight percent, and an acid value of from about 179 to about 192, whereas a desired acid value ranges from about 194 to about 200. Accordingly, downstream products containing carboxylic acid functionality made from fatty acids of low acid value will also have a low acid value which in turn, reduces the quality and commercial value of such products.
The present invention addresses and avoids the aforementioned problem, i.e., esterification of fatty acids by stripping at relatively high temperature, by providing methods of recovering free fatty acids having a reduced ester content and increased acid value relative to the ester content and acid value of fatty acids obtained by stripping fatty acid mixtures at relatively high temperatures to remove the alkanol and solvents.
The methods described herein are advantageous in that the recovered fatty acids are a by-product of the aforementioned tocopherol recovery method and as such, offers a less expensive, high quality (high acid value) starting material for production of dimerized fatty acids, isostearic acid, and other commercially valuable products of high quality.
A method for recovering free fatty acids from an alkanol-containing solution of the fatty acids is provided which comprises distilling the alkanol-containing solution under conditions of temperature and pressure sufficient to avoid any appreciable production of fatty acid esters to provide a product containing free fatty acids and no appreciable amount of fatty acid esters.
A method of separating fatty acids from a composition containing at least one non-saponifiable component is also provided which comprises a) subjecting the composition to saponification conditions in the presence of alkali metal hydroxide, alkanol and water to provide a mixture containing at least one non-saponified component and saponified fatty acids, b) separating the mixture by solvent extraction employing a solvent to provide a solvent-rich phase containing the non-saponified component(s) of the mixture and a raffinate phase containing the saponified fatty acids, alkanol, water, the balance of the solvent and alkali metal hydroxide, c) acidifying the raffinate phase to provide an aqueous phase containing water, alkanol, and alkali metal salt and an organic phase containing fatty acids, alkanol, and solvent, and d) distilling the organic phase under conditions of temperature and pressure sufficient to avoid the production of any appreciable amount of fatty acid esters to provide a product containing fatty acids and no appreciable amount of fatty acid esters.